Different telecommunication transport schemes are used to implement communication networks. For example, Ethernet is typically used to provide communications within local area network (LAN) environments. Ethernet has become the standard for LANs and is generally available in four bandwidths: the original 10 Mbps system, 100 Mbps Fast Ethernet (IEEE 802.3u), 1,000 Mbps Gigabit Ethernet (IEEE 802.3z/802.3ab), and 10 Gigabit Ethernet (IEEE 802.3ae). Synchronous Optical Network (SONET) or the Synchronous Digital Hierarchy (SDH), as it is known in Europe, is used to transport communications throughout wide area network (WAN) environments.
SONET/SDH is recognized as a practical way to link high speed Ethernet networks over WANs. A persistent problem with transporting Ethernet over SONET (EOS) is inefficient use of system resources. For example, SONET was designed to carry DS1 (1.544 Mbits/sec) and DS3 (44.736 Mbits/sec) signals. Beyond the STS-3 (155.520 Mbits/sec) rate, SONET grows by a factor of four. The fundamental Ethernet rates do not support DS1 or DS3 rates and grow in multiples of ten. As a result, the various Ethernet transmission rates (10 Mbps, 100 Mbps, 1,000 Mbps, and 10,000 Mbps) do not map well into SONET/SDH frames.
For example, the original 10 Mbps Ethernet signal is too small for an entire STS-1 (51.84 Mbps) path. Under existing SONET/SDH schemes, an entire STS-1 path is needed to transport a 10 Mbps Ethernet signal. The rate mismatch between SONET and Ethernet results in large bandwidth inefficiencies. In other words, a significant amount of bandwidth is wasted by linking high speed Ethernet networks using SONET/SDH frames. Similar inefficiencies results when attempting to map the faster Ethernet signals into STS signals.
A Virtual Concatenation (VCAT) Protocol was created to efficiently map Ethernet signals into SONET/SDH frames. VCAT increases efficiencies by allowing SONET payloads to combine into a single, virtual payload. For example, VCAT combines multiple signals (members) into one Virtual Concatenation Group (VCG), enabling the carrier to optimize the SDH/SONET links for Ethernet traffic. For example, Two STS-1 (51 Mbps) signals can be combined to carry a 100 Mbps Ethernet signal. VCAT uses SONET/SDH overhead bytes to indicate two numbers: the multiframe indicator (MFI) and the sequence number (SQ). The VCAT intelligence resides at endpoints of SONET paths, so the SONET network does not need to have knowledge of VCAT.
Individual members of a VCG may traverse different network paths while traveling between endpoints, e.g., an origination point and a destination point. Thus, members may arrive at their destination out of order and with different delays. This situation is generally referred to as “skewing”. In order to reassemble the members of a VCG in proper order without undue delay and without losing any members, the arriving members must be buffered and de-skewed. De-skewing uses the multi-frame indicator (MFI) as a time stamp to align all of the VCG members. In its simplest form, de-skewing involves placing members of a VCG in a buffer until the member with the most delay is received. When all members of a VCG are received, they are read out of the buffer in the proper order. Typically, the members are written to RAM with an address based on their MFI numbers.
During a service interruption, SONET/SDH technology is able to detect and restore a connection. For networks having few connections, service restoration may occur virtually instantly, i.e., 50 milliseconds. For networks having many connections, service restoration may take several seconds. As such, reducing the number of connections between endpoints reduces setup connection times or service restoration times when recovering from service disruptions. Therefore, what is needed is a system and method for reducing the number of connections between endpoints while still supporting VCAT.